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The elevated temperature strength of multicomponent Al-Si alloys is greatly affected by the volume fraction and the interconnectivity of hard phases formed upon solidification. In the present investigation, such influences were examined for two Al-Si-Cu-Ni alloys with different total volume fractions of hard phases. To control the microstructural features related to the size of the phase, the specimens were prepared with and without ultrasonic melt treatment (UST) at different cooling rates. The microstructures of the alloys were composed of primary Si, eutectic Si, (Al,Si)3(Zr,Ni,Fe), Al9FeNi and Al3(Cu,Ni)2 phases. The microstructural features, such as the size and aspect ratio of each phase, changed with UST and cooling rate, and accordingly, the elevated temperature strength at 350 ℃ was changed. The alloy with a high volume fraction of about 30 vol.% exhibited increased elevated temperature strength at 350 ℃ when ultrasonic melt treated, and the alloy having a volume fraction as low as about 18 vol.% exhibited the opposite results. Considering the microstructural features of the multi-component Al-Si alloy, a hexagonal shear-lag model was suggested, based on the well-known shearlag model proposed by Nardone and Prewo (Scr. Metall. 20;1986:43-48). Using the 2-D microstructural factors such as the size, aspect ratio of the phase and secondary dendrite arm spacing, the elevated temperature strength was calculated and compared with the measured value. Based on the hexagonal shear-lag model, the influence of microstructural factors on the elevated temperature strength was discussed for multi-component Al-Si-Cu-Ni alloys. (Received 4 November, 2021; Accepted 12 April, 2022)

keyword : Al-Si-Cu-Ni alloy, elevated temperature strength, interconnectivity, microstructure, ultrasonic melt treatment, cooling rate

There is growing interest in the recovery of pure palladium (Pd) compound from cemented Pd from spent electroplating solutions due to increasing demand for Pd, and there is considerable motivation to develop an efficient recovery process. In conventional methods of leaching Pd metal, HCl solutions containing oxidizing agents are employed. In this work, ethylene glycol (EG) replaced water as a diluent in the HCl solution containing oxidizing agents such as H₂O₂, NaClO and NaClO₃. Leaching of the Pd metal and the subsequent precipitation of the Pd(IV) compound was investigated. Among the three kinds of oxidizing agent, NaClO₃ showed the best Pd metal leaching efficiency from a metallic mixture of Pd and Zn from HCl in EG solution. The role of EG in enhancing the leaching and precipitation is discussed in light of its interaction with other components in the solutions. To precipitate the Pd(IV) compound with NH₄Cl, it is important that the dissolved Pd ion exists as Pd(IV). Therefore, NaClO₃ was again added to the leaching solution to verify the oxidation of Pd(II) to Pd(IV). Extra pure ammonium hexachloropalladate ((NH₄)₂PdCl₆) was recovered by precipitation from the leaching solution of the cemented Pd under the optimum conditions. Compared to conventional HCl systems, the present process shows some advantages, by reducing both chemical dosage and energy consumption. The results confirm a process can be developed for the recovery of the Pd(IV) compound from spent electroplating solutions containing a small amount of Pd(II). (Received 24 February, 2022; Accepted 31 March, 2022)

keyword : ethylene glycol, leaching, precipitation, palladium, ammonium heaxachloropalladate

In this study, ultrathin (4-40 nm) Cu-layer-based transparent heaters prepared on glass substrates were investigated for cost-effective applications. The Cu heaters were embedded between ZnO layers serving as anti-reflection and anti-corrosion layers. The Cu layer thicknesses varied in the range of 4-40 nm, and the corresponding structural, electrical, optical and thermal properties were evaluated. Cu was found to follow the Volmer-Weber 3D growth mode in the early deposition stage, where isolated islands grow and coalesce to form a continuous layer at ~12 nm. In the thickness regime of discontinuous Cu layers, a significant increase in sheet resistance was observed due to the reduced current paths and the high severity of electron scattering at the Cu/ZnO interfaces. Because of light absorption associated with the localized surface plasmon resonance (LSPR) in the presence of pores in the films, visible transparency peaks near the thickness of the complete film-closure, beyond which stronger light absorption decreases transparency. The sheet resistance of the transparent heaters was modulated in the range of 0.8-96.2 Ω/sq. The heating characteristics well follow Joule’s law which predicts a higher temperature for a lower-resistance heater at a given voltage. The measured temperature-power relation is linear, from which the important heater parameter of convective heat transfer coefficient is extracted. (Received 28 March, 2022; Accepted 27 April, 2022)

keyword : copper, thin films, transparent heaters, electrical resistance, optical transmittance

Improving solar energy conversion efficiency and reducing energy loss have become critical issues in recent decades. Photoelectrochemical (PEC) water splitting provides an ideal method for solar energy harvesting and is a key factor in decreasing the use of fossil fuels. Thus, it is extremely important to identify cost-effective, highly active, and robust semiconducting photoelectrodes that can reduce the overpotential reaction and increase electrocatalytic efficiency. However, for overall water splitting, it is challenging to identify suitable photocatalysts with efficient band structures and suitable charge separation for electron-hole pairs. Water splitting is conventionally performed using independent layer-by-layer (LBL) or hydrothermal (HT) techniques. However, this research aims to produce a photoanode by applying both HT and LBL methods in sequence to reduce energy loss during the electron transfer process between the two photosystems. In this study, a TiO₂ layer was deposited onto fluorine tin oxide (FTO) glass using the LBL method (TiO₂/FTO). Subsequently, hematite (α-Fe₂O₃) thin films that were synthesized using the HT method were deposited onto TiO₂/FTO glasses (Fe₂O₃/TiO₂/FTO). The as-prepared and newly-designed photoanode Fe₂O₃/TiO₂/FTO demonstrates a significantly high photocatalytic activity of 7.68 mA/cm². Thus, by combining the HT and LBL methods, excellent hydrogen production performance in regard to photocatalytic water splitting was achieved. Furthermore, this hierarchical structure provides good chemical stability and is an excellent candidate for large-scale applications. (Received 4 January, 2022; Accepted 30 March, 2022)

keyword : photoelectrochemical water-splitting, semiconductors, hematite (α-Fe_{2O3), Ti doping, hydrothermal method, doping method}

Unlike conventional solid oxide fuel cells (SOFCs) where ceramic materials have been used as a support, in this study a new SOFC structure with a metal support and a contact layer between the support and anode is suggested. A mixture of Ni-Fe alloy and zirconia ceramics as the contact layer were employed to enhance the compatibility of the metal support and the anode (Ni-zirconia). Common materials, including acceptor-doped zirconia and perovskites (Ba-Sr-Co-Fo-O, La-Sr-Mn-O), were used for the solid electrolyte and cathode of the SOFC. The electrode polarization resistance of the metal-supported SOFC manufactured in this way depended on the resistance between the cathode and electrolyte. For the SOFC with a Ba-Sr-Co-Fe-O cathode, not only large polarization resistance but also large ohmic resistance occurred due to the formation of an insulator phase on the surface of the solid electrolyte. Consequently, it exhibited low fuel cell performance (power density ~ 40 mW/cm² at 750℃). On the other hand, a high fuel cell performance of ~ 290 mW/cm² was achieved for the SOFC with the La-Sr-Mn-O cathode. The ohmic resistance was affected by the metal support and the contact layer. (Received 21 March, 2022; Accepted 2 May, 2022)

keyword : metal-supported SOFC, Ni-Fe alloy metal support, contacting layer, perovskite cathode

Modulation doping occurs in a heterojunction where a charge carrier-rich material transfers charge to a carrier-deficient material. The modulation-doped material is intentionally selected to have higher charge carrier mobility than the modulation dopant material, so that the overall electrical conductivity can be boosted. Although this modulation doping strategy has proven effective in enhancing power factor in thermoelectrics, selection criteria for such semiconductor couples have not been explicitly clarified, resulting in only a few discovered semiconductor couples available for modulation doping-driven thermoelectric systems [1-4]. Here, we (i) report an electronic band structure-based guideline to actualize modulation doping, (ii) reveal that hole-rich PEDOT:PSS can modulation dope otherwise undoped tin monosulfide (SnS) in their bilayered structure, (iii) prove that modulation doping is responsible for thermoelectric power factor enhancement by comparing computational and experimental Seebeck coefficient and electrical conductivity values. The optimized PEDOT:PSS thin film / SnS pellet bilayered structure had a 134.7 fold improvement in electrical conductivity and a 93.6 fold power factor enhancement over those of undoped SnS, with only a ~ 20 % decrease in Seebeck coefficient. The modulation doping effect can result in further power factor improvement when SnS becomes a nanoscale thin film or nanoparticles in the future. (Received 22 March, 2022; Accepted 2 May, 2022)

keyword : modulation doping, PEDOT:PSS, tin monosulfide (SnS), seebeck coefficient, power factor, electrical conductivity

Hydrogen is considered an attractive energy resource because it is eco-friendly in contrast with fossil fuels. Hydrogen storage remains as essential technology for increasing the use of the hydrogen in applications such as hydrogen vehicles and fuel cells. Hydrogen storage requires retaining a high density of hydrogen molecules at ambient temperature in a suitable tank. Zeolites are one of the promising hydrogen storage materials, but experimentally investigating them for hydrogen storage is difficult since the number of the zeolites in the largescale material database has been increasing. In the present study I developed an efficient method of exploring potential zeolites in the database that had high volumetric hydrogen storage capacity. To do this I employed a high-throughput screening approach to automatically construct a zeolite database for hydrogen storage in the Inorganic Crystal Structural Database (ICSD). Also, I performed grand canonical Monte Carlo (GCMC) simulations to estimate hydrogen adsorption isotherms at operating ambient temperatures, to determine the volumetric hydrogen storage capacity of the zeolites. Finally, I found 10 top ranked materials in the zeolite database for H₂ storage, and I calculated Pearson’s correlation coefficient to revealed the linear correlations between the hydrogen storage capacities and 3 structural characteristics (i.e., surface area, largest cavity diameter, pore limiting diameter). Furthermore, I investigated atom species in the 10 materials to show the relation between the hydrogen storage capacities and chemical elements. In future works, I expect the method can be easily applied to accelerate the discovery and design of porous materials for storing CO₂ or toxic gases. (Received 28 January, 2022; Accepted 18 April, 2022)

keyword : hydrogen storage, porous material, zeolite, high-throughput screening, adsorption isotherm

This study investigated the photovoltaic properties and microstructure of perovskite solar cells (PSCs) with an ITO/SnO₂/perovskite/HTL/Au electrode configuration, developed with varying sintering temperatures (100~200℃). The goal was to use SnO₂ ink as the electron transport layer (ETL) by lowtemperature sintering. TGA-DTA analysis was conducted to determine the optimum sintering temperature of the SnO₂ ink and the photovoltaic properties were examined by solar simulator analysis. To analyze the microstructure, a 3D profiler, optical microscope, and scanning electron microscopy (SEM) were used. The TGA-DTA analysis results show that SnO₂ ink was effectively sintered at the low temperature of 80℃ and above. As for the photovoltaic(PV) properties, the PV efficiency was approximately 15% at 120~150℃, and increased to a maximum of 17.16% at 180℃, and then fell to 12% at 200℃. The RMS value, a representation of surface roughness, of the SnO₂ layer according to sintering temperature incrementally decreased, reached its lowest at 180℃, before finally increasing. The microstructure analysis showed that the perovskite layer formed on the SnO₂ at a sintering temperature of 180℃ had a relatively greater grain size of 402 nm and a thickness of 432 nm, thereby improving the PSC’s PV properties. These results suggest it is possible to implement a PCS with SnO₂ ETL by low temperature sintering process. (Received 23 February, 2022; Accepted 5 April, 2022)

keyword : SnO_{2 ink, low temperature sintering, MAPbI3 perovskite, roughness}

High quality Hg₂Br₂ crystal grown via the physical vapor transport (PVT) process is essential for the fabrication of the acousto-optic tunable filters (AOTFs) module. The full process flow, including powder purification and crystal growth, should be systematically established, but there have been few reports about the fully established process flow of single Hg2Br2 crystal. In this study, we report on the entire process, from purification of the Hg₂Br₂ powder to crystal growth based on the PVT process. We compared the raw powder and purified powder using X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma (ICP). Although there was no considerable difference in the XRD and XPS results of the powders before/after purification, the ICP impurity analysis indicated that the purity of Hg₂Br₂ powder increased from 4N (99.99%) to 5N (99.999%). The Hg₂Br₂ single crystal grown by the PVT process was then fully characterized by XRD, XPS, and Raman spectroscopy. The vibration bonds constituting the Hg₂Br₂ lattice were clearly identified from the Raman spectra of the final Hg2Br2 crystal. High quality Hg₂Br₂ single crystal PVT-grown from the purified powder will lead to the development of a high-performance acousto-optic module. Establishing the systematic growth sequence of the Hg₂Br₂ based on PVT paves the way to promising AOTF modules. (Received 23 March, 2022; Accepted 12 April, 2022)

keyword : Hg_{2Br2, acousto-optic single crystal, powder purification, crystal growth, physical vapor transport}